Scanners are widely used to process image information into digital forms. Scanners are generally classified as two major types: transmissive scanners and reflective scanners for scanning opaque and transparent objects, respectively. Examples of the opaque objects include paper sheets, photographs, etc., and the common transparent objects are for example slides and films. For capable of scanning both opaque and transparent objects, a dual-mode scanner for optional transmissive/reflective scanning was developed. Referring to FIG. 1, a conventional dual-mode scanner is schematically shown. When the scanner is operated in the reflective mode, light emitted by a lamp 12 positioned at the same side as the carriage module 11, i.e. in the lower housing 101 of the scanner, is projected onto the surface of the opaque object 14 to be scanned. The light reflected from the opaque object 14 is then transmitted into the carriage module 11 to be processed. The reflected optical signal indicative of the image information is converted into an electric signal via a photoelectric conversion device (not shown) in the carriage module 11, and then the electric signal is further processed digitally. When the scanner is operated in the transmissive mode, light is emitted by a lamp 13 positioned at opposite side to the carriage module 11, i.e. in the upper housing or cover 102 of the scanner. The light penetrates through the transparent object 15 to be scanned, and then received by the carriage module 11 to be converted into an electric signal. Then, the electric signal is outputted to a processing device (not shown) such as a computer to be processed digitally.
As understood in the above description, there are two lamps 12 and 13 positioned at both sides of the scanning platform 16 required. If the opaque object 14 is being scanned, only the reflective lamp 12 is turned on. The light emitted from the lamp 12 is projected onto the surface of the opaque object 14, and reflected from the opaque object 14 into the carriage module 11 to be converted into an electric signal. On the contrary, if it is the transparent object 15 to be scanned, only the lamp 13 is turned on. The light emitted from the lamp 13 passes through the transparent object 15 to be received by the carriage module 11 and converted into an electric signal.
Since the above mentioned dual-mode scanner needs two individual lamps, the cost and the size thereof are undesirably high.